Treatment of Infertility by Acupuncture According to Circalunar and Cardiac Variability Rhythms
A part of this paper was presented at WFAS International Acupuncture Congress, cosponsored by World Health Organization, in Beijing, China, Oct. 2007.
Page updated on January 31, 2008
Acupuncture has been used to treat various gynecological and reproductive problems over the centuries in the Orient . Acupuncture use in Western countries has sharply increased since 1970, mainly as an adjunct modality for chronic pain management. More recently however, use of acupuncture has expanded widely for a variety of health problems.
In the area of female health and fertility, acupuncture has been shown to be beneficial for women with PCOS and anovulation , and it has been shown to increase uterine blood flow . Acupuncture has also been shown to decrease the symptoms related to endometriosis  and primary dysmenorrhea [5, 6]. In several recent years, a growing number of research publications investigating the efficacy of acupuncture on infertility, have been appearing in peer-reviewed medical journals. Most of the papers, however, are particularly focused on the use of acupuncture in conjunction with IVF [7-12]. In April 2002, Paulus et al. from Germany reported that they had produced a higher clinical pregnancy rate in women undergoing IVF using acupuncture compared to IVF without acupuncture (42.5% versus 26.3%) .
Medline indexed English articles on infertility and acupuncture from 1981 to 2007
Upon the German researcher’s success, several groups attempted to replicate their results. Two randomized trials published in 2006 also found higher IVF pregnancy rates compared with standard IVF without acupuncture  or compared with patients who received ‘placebo’ acupuncture . The latter study, by Westergaard et al., also employed a 2nd acupuncture group in which patients received additional acupuncture 2 days after their embryo transfer. This additional treatment did not produce any significant changes in outcome. A ‘placebo’ controlled trial by Smith et al. did not show significant benefit of acupuncture for IVF outcome . Paulus et al. then conducted a second study using placebo needles which did not indicate a significant difference between the real and placebo acupuncture groups . Finally, in the fall of 2007, a University of Oklahoma group apparently* reported that they found a lower pregnancy rate among women who received the German acupuncture protocol (*Based on a news release. The original paper is not yet available, as of Jan. 2008). Despite a growing number of studies on infertility and acupuncture, the scientific basis for this therapy is still in its infancy. More studies on laboratory animals and human trials are certainly needed in order to further clarify the mechanism and efficacy of acupuncture.
‘Placebo’ versus ‘real’ acupuncture
Outcomes of acupuncture trials can be quite different (positive or negative) depending on what type of acupuncture methods and controls (placebo) are used. This could be one of the reasons why some of the previous acupuncture trials done on the same disease or condition yielded conflicting results. Furthermore, different interpretation of results can be made depending on how ‘placebo’ or ‘real’ acupuncture is defined.
In pharmaceutical trials, a placebo pill (which looks exactly the same as the trial drug but is without active ingredients) is used to create equilibrant psychological impact to the patients (and doctors) as the actual drug. Developing ‘placebo’ acupuncture that mimics real acupuncture is much more complex than placing sugar in a gelatin capsule. Different variations of ‘placebo’ or ‘sham’ acupuncture interventions have been proposed and used by many researchers. The ‘placebo’ acupuncture used by researchers in infertility trials [11-13] was a procedure involving acupuncture needles inserted on sham points that are not considered to enhance fertility. It should be emphasized that the ‘placebo’ acupuncture utilized by these previous studies is not physiologically inert and should not be considered as an adequate control [14-17].
So what is ‘real’ or ‘genuine’ acupuncture? The fact of the matter is that a wide variety of acupuncture styles exist and procedures vary even among professional acupuncturists. The ‘real’ acupuncture used in many of the previous infertility studies is different from the procedures commonly used by acupuncturists according to acupuncture educators in the USA . For example, electro-acupuncture has been widely used in acupuncture research in animal and human models because the amount and intensity can be standardized and more easily controlled than manual acupuncture. Electro-acupuncture however, is not the most commonly practiced form of acupuncture in a clinical setting for treatment of infertility . Further, many previous acupuncture studies on infertility administered only a few standardized treatment sessions. Most acupuncturists in the clinical setting however, utilize non-standardized treatment protocols (points, methods of stimulation, etc.) based on each patient’s individual conditions and administer a series of treatments throughout weeks or months . There was a series of studies in Japan which reported increased fertility rate including in intractable infertility cases with regular long-term (> 3month) administration of acupuncture [20, 21]. Repeated acupuncture treatment is believed to produce cumulative effects over time.
Due to such a wide diversity of acupuncture treatment methods, circumspect consideration is necessary when interpreting the results of acupuncture studies. The results obtained by using one acupuncture method may not be applicable when a different acupuncture method is administered. There is no established standard acupuncture protocol for infertility and the efficacy and safety of different acupuncture methods needs to be clarified by comparative studies in the future. Nevertheless, considering the empirical nature of acupuncture, clinical experience of acupuncturists will likely remain as one of the most crucial elements for achieving highly effective and satisfactory clinical outcomes.
Acupuncture treatment for infertility according to circalunar menstrual rhythm
The acupuncture system used at The Pacific Wellness Institute is a holistic treatment system and symptoms are considered to be a manifestation of the body’s disharmony. Treatment is based on each individual’s constitution, Western diagnosis (i.e. endometriosis, PCOS, thin lining, high FSH, etc.), and whether or not the woman is conceiving naturally or in conjunction with modern fertility treatment (i.e. hormone administration, IUI, IVF, etc.). The exact location of the needles varies between each individual; however, in general, needling points are chosen on the entire body regardless of health condition. Female hormones are centrally regulated through the hypothalamus-pituitary axis; thus, ‘systemic regulation points’ are always included as an important part of treatment. A SES technique (repetitive superficial needling stimulation applied synchronically with autonomic alteration upon respiratory and postural changes), for example, has been shown to induce a systemic reaction mainly through activation of vagal nerves [22, 23]. Our treatments are complimented with other empirical techniques such as indirect moxibustion. Over thousands of years, moxibustion has traditionally been used in conjunction with acupuncture. Indirect moxibustion is used to increase local blood flow and to further promote the relaxation response.
Selection of acupuncture points for fertility
In addition to systemic acupuncture treatment, we utilize more specific treatment points for various fertility situations for patients who have fertility concerns. For many women, the menstrual cycle is typically divided into 4 phases: menstruation, follicular (pre ovulation), pre-implantation (ovulation) and luteal phases. During each phase, a different combination of acupuncture points and stimulation methods are used to maximize the potential benefits and safety of each treatment. For patients undergoing modern fertility treatment such as IVF or IUI, the acupuncture treatment is modified according to the stage of fertility treatment.
While selection of acupuncture points varies between patient to patient and session to session, in general, points are chosen based on both Eastern meridian theory and Western anatomy (autonomic nerve innervations).
- Ancient Chinese medicine: There are several well known acupuncture points that are traditionally used to influence reproductive organs (e.g. conception vessel 2-4 in the low abdomen, spleen 6 near the ankle, and other points along spleen, liver, kidney, bladder meridians and conception vessel).
- Western anatomy/physiology: From a Western anatomical perspective, acupuncture points along T11 to L2 dermatomes (sympathetic, mainly lower abdominal, low back and upper buttock areas) and S2 to S4 (parasympathetic, mainly sacrum, buttocks, and back of the legs) dermatomes are the focus, according to autonomic nerve innervations to female reproductive organs . A series of experiments conducted by a group of Japanese and Swedish researchers demonstrated that stimulating different spinal and sacral nerve segments in a specific manner increased or decreased blood flow of ovaries or uterus [3, 25-27]. Those research findings have profound implications for the treatment of various fertility problems.
Acupuncture stimulation methods
It is important to note that effectiveness of acupuncture is not solely dependent on selection of acupuncture points, but also on other factors such as depth of needle insertion and intensity of stimulation. At The Pacific Wellness Institute, needles are superficially inserted (2-3 mm in depth) and manually stimulated in most cases. Previous experiments suggest that superficial needling stimulates the receptors in skin and subcutaneous tissue as one of the crucial elements in inducing a parasympathetic activation response . This is important because while the exact mechanism of how acupuncture enhances fertility is not known, the involvement of relaxation response through modification of autonomic nervous system balance (sympathetic and parasympathetic) has been frequently suggested [19, 28].
The pelvic viscera contain dense autonomic fibers . The acupuncture treatment used at The Pacific Wellness Institute is targeted to balance the autonomic nervous system and enhance blood flow to reproductive organs. It has been demonstrated in experiments using rats, that excitation of α-adrenergic receptors causes a decrease of uterine and ovarian blood flow [25-27]; whereas, an excitation of parasympathetic nerves will increase uterine blood flow . Our acupuncture treatment is a virtually non-invasive procedure involving an extremely gentle superficial needling technique that is targeted to elicit relaxation through activation of a parasympathetic response. It is important to note that stress-induced neural and hormonal response (i.e.: sympathetic activation, increased plasma cortisol, adrenalin etc.) may negatively influence reproduction [29, 30]. Thus, in most cases, acupuncture administration should be very gentle and ‘painless’; intense and deep acupuncture needling technique that cause unpleasant pain or stress to patients should generally be avoided.
Acupuncture and Sound Assisted Autonomic Modulation Technique
Utilizing our custom made CDs, this technique directs patients to breathe in a specific rhythm (frequency between 0.08-0.12 Hz) while lying on the table with acupuncture needles inserted. For most patients, the targeted breathing rate is approximately 6 breaths per minute (0.1Hz.). During the treatment sessions, either the patient’s index finger or ear lobe is connected to a photoplethysmography probe in order to monitor autonomic response during treatment. The heart rate frequency spectrum is evaluated and feedback is provided to the patients.
While most people find this breathing exercise relaxing, and it can certainly be used as a powerful stress management tool, the intention with this breathing exercise and the response it induces is different than common relaxation methods. As shown in Figure 1, the distinct pattern of heart rate seen in the last 15 min. (a larger variability with a more coherent rhythm) typically cannot be induced by practicing commonly used relaxation methods. When the heart is beating in such a pattern (a coherent rhythm and high variability), the autonomic and hormonal reflexes are actively stimulated. This leads to enhanced modulation in our internal system. Potential implications to a variety of autonomic and hormone related disorders have been suggested .
Since 2002, at The Pacific Wellness Institute, the HRV based breathing exercise has been actively used in conjunction with specific acupuncture procedures targeted to provide stimulus to the autonomic nervous system. Clinical results obtained with this combined approach are noteworthy, not only on autonomic disorders but also when the condition is associated with disturbance in chronobiological rhythms (e.g., certain forms of insomnia and menstrual irregularities).
Concept of Chronobiology
Our internal physiological functions are constantly fluctuating in various rhythmic fashions. The most well known rhythm in chronobiology is the circadian rhythm – a roughly 24-hour cycle seen in the physiological processes of plants and animals. In humans, clear alteration of the hormone melatonin can be observed in a nearly 24-hour rhythm. Ultradian rhythms are shorter cycles (<20 hr), such as the 90-minute REM sleep cycle. Female hormones alter according to the menstrual cycle which is approximately 28 days. This rhythm is referred to as a circatrigintan or circalunar rhythm. Studies have suggested that disrupted circadian rhythmicity occurs in shift work or increased nocturnal exposure to light and is associated with menstrual irregularity and infertility .
Chronobiology is the study of these biological rhythms. “Chrono” pertains to time and “biology” pertains to the study, or science of life. Chronobiology examines periodic (cyclic) phenomena in living organisms and their adaptation to solar and lunar related rhythms. This field interacts with a variety of medical research fields such as jetlag, sleep disorders, endocrinology, sports medicine, cardiology and space medicine. Interestingly, the core concept of the rather newer field of medicine, mirrors the foundational philosophical paradigm of ancient Chinese medicine, which evolved over two thousand years ago.
Summary of outcomes between January 2004 and December 2005
A growing number of patients visited our clinic seeking acupuncture for their fertility difficulties. Administrative and basic medical records of patients were managed by Microsoft Access database. Data of female patients with their ongoing fertility concerns, who visited our facility between January 2004 and December 2005, were extracted from the database, and then each patient’s file was further examined. Patients who received at least two acupuncture treatments were included for further analysis. Most of the acupuncture sessions were provided by the author who has obtained acupuncture training and licensing in Japan, and who has had over 20 years of clinical experience.
For patients who received acupuncture during their IVF cycle, outcomes were evaluated by sending a letter requesting the outcome of a pregnancy test. For all other patients attempting to conceive either naturally, assisted with hormone administration or with intrauterine insemination (IUI), outcomes were determined by volunteer self-reporting following pregnancy or post term. Self-reporting included contact through telephone calls, letters, and visits to the clinic.
Analysis of these patients showed a total of 76 pregnancies. Among those, 34 were naturally occurring pregnancies, 12 were through IUI, and 30 were through IVF procedures. In 13 out of 76 (17 %) total pregnancy cases, some male partner abnormality was reported (i.e.: low sperm count, low motility, poor morphology, high DNA fragmentation, etc.). 17 out of the 59 (29%) total non-pregnancy cases reported male abnormality. The average age at the first visit for the pregnancy group was 35.9±4.1; whereas for the non-pregnancy group it was 35.6±3.7. The mean number of acupuncture treatments received prior to first pregnancy was 9.7±5.7 (3-27 visits) for natural, 15.3±7.4 (6-32 visits) for IUI, and 15.8±8.4 (2-36 visits) for IVF.
34 natural pregnancy cases (Patients who conceived without assisted reproductive therapies) were confirmed through self initiative reporting by patients (ie: visit to the clinic, telephone, e-mail, etc.). Except for 4 cases, in which patients were taking either follicle-stimulating hormones and/or progesterone during the pregnancy cycle, all other natural pregnancy cases achieved conception without any fertility drugs. There was 1 case in which the patient became pregnant in the following menstrual cycle after treatment was ceased. In all other cases (n=33), patients received acupuncture during the pregnancy cycle. There were 2 patients who became pregnant twice (both carried to term following an initial miscarriage), and one patient who became pregnant three times (2 miscarriages, status of 3rd pregnancy unknown) during the study period.
Many of the patients had underlying gynecological or hormonal related conditions which potentially interfered with conception (ie endometriosis, an elevated prolactin level, hypothyroidism, fallopian tube obstruction, an elevated day 3 FSH level, autoimmune disorders, PCOS, etc.). Ten out of 34 patients who became pregnant naturally had some kind of pre-existent fertility condition (29%), as compared to 6 out of 13 patients who did not conceive had underlying conditions (46%).
Regarding pregnancy rate using acupuncture
Computing ‘success rate’ for infertility is not as simple as using the mathematical formula: X (total number of pregnancy) divided by Y (total number of patients). There are a number of methodological difficulties regarding success rate statistics and no standardized guideline exists to calculate the success rate of acupuncture for infertility cases. Some of the issues and variables to consider when calculating statistics are as follows:
Infertility success rate largely depends on the sample population. Infertility is caused by a variety of factors and it is well known that fertility rates vary significantly depending on factors such as age and co-existing medical conditions. Also, it is necessary that separate statistics be produced for patients who conceived naturally with acupuncture and for patients who underwent assisted reproductive technologies (ART) or any other medical fertility treatment in conjunction with acupuncture. Other important factors are how dropout cases are counted and determination methods of ‘pregnancy’ (i.e. blood test, US, carry to term, etc.). Lastly, statistics derived from an insufficient number of cases in each group contain a large margin of error. These are just a few examples of methodological difficulties regarding success rate statistics.
Thus, although we do monitor outcomes of our patients and occasionally conduct preliminary analysis for our own critical evaluation and professional education purposes, we do not make ‘success rate’ available to the public due to obvious ethical concerns. Statistics can be easily manipulated and success rate can vary greatly depending on the sample population, criteria and rules used when calculating the statistics.
A growing number of patients visited our clinic seeking acupuncture for their fertility difficulties. Patients who visited our clinic during the two year period between Jan. 1 2004 and Dec. 31 2005 for their ongoing fertility concerns were examined.
It should be noted that while the majority of IVF patients reported pregnancy after ultrasound showing fetal heart beat (57%) or post delivery (25%), some others reported positive beta HCG test(s) results only (18%). This is one of the limitations of this study. It is also important to note that IVF outcomes vary greatly depending on factors such as patient’s age, medical background, partner’s sperm quality, types of IVF (fresh, frozen, use of donor eggs, etc.) and IVF program attended. In order to draw any conclusion about the extent, if any, that acupuncture impacted the outcome, it is necessary to design a prospective randomized study with a control group containing comparative patients’ backgrounds and IVF procedures. Pregnancy rates across the different age groups are not provided in this paper due to small sample sizes. Pregnancy rate data for natural and IUI cases is not included in this paper due to methodological difficulties (small sample size, missing data, drop out cases, transferred to IVF, etc.).
Although it is well known that advancement of age is negatively associated with conception rate, in this study there was relatively no difference between pregnancy (35.9 years ±4.1) and non-pregnancy group (35.6 years ±3.7). Subcategorized comparison among natural, IUI, and IVF patients also did not show any average age differences between pregnant and non-pregnant group. There were 34 natural pregnancy cases without use of ART. Mean number of acupuncture treatments received prior to first pregnancy was lower (9.7±5.7 visits) for natural compared to IUI (15.3±7.4 visits) and IVF (15.8±8.4 visits) groups. It should be stated that a substantial number of patients who had initially intended to conceive naturally moved on to IUI or IVF after a few natural cycles with acupuncture. This is likely one of the main reasons why the average number of treatments prior to pregnancy is lower among natural pregnancy cases. Many other patients, however, elected not to proceed to IVF or other ART interventions due to various reasons (medical, financial, religious, etc.) and chose to attempt to conceive naturally with acupuncture sessions over a number of cycles. Some of those patients eventually conceived naturally following a number of acupuncture sessions (over 25 sessions).
There were 3 patients who were receiving acupuncture for their upcoming IVF cycle when they conceived naturally. These were considered extremely difficult cases without assistance of IVF: Two cases had been recommended donor egg IVF due to previous IUI and IVF failures which were possibly related to their advanced age. Bilateral fallopian tube blockage had been indicated in one case. Those pregnancy cases are certainly intriguing and similar remarkable successes have been continuously observed from time to time in our facility. However the mechanisms of how acupuncture worked are unknown and these cases should be considered exceptional until more solid, non-anecdotal data becomes available.
In conclusion, although the overall clinical result at The Pacific Wellness Institute seem favorable and quite promising, the previous randomized clinical trials, conducted at different facilities, have yielded conflicting outcomes. Difference in sample populations, trial protocol, various confounding factors, and type of acupuncture used (points, stimulation methods, frequency, duration, training/experience of acupuncturists, etc.) could be attributed to the ambiguous results. The results described in this paper are based on retrospective clinical observation study. Carefully designed prospective RCTs and consequent systematic review are required in order to clarify the efficacy of acupuncture for female infertility.
1. Maciocia G: Obsteterics and gynecology in Chinese medicine. New York: Churchill Liningstone, 1998.
2. Stener-Victorin E, Waldenstrom U, Tagnfors U, Lundeberg T, Lindstedt G, Janson PO: Effects of electro-acupuncture on anovulation in women with polycystic ovary syndrome. Acta Obstet Gynecol Scand 2000; 79(3): 180-8.
3. Stener-Victorin E, Waldenstrom U, Andersson SA, Wikland M: Reduction of blood flow impedance in the uterine arteries of infertile women with electro-acupuncture. Hum Reprod 1996; 11(6): 1314-7.
4. Highfield ES, Laufer MR, Schnyer RN, Kerr CE, Thomas P, Wayne PM: Adolescent endometriosis-related pelvic pain treated with acupuncture: two case reports. J Altern Complement Med 2006; 12(3): 317-22.
5. Helms JM: Acupuncture for the management of primary dysmenorrhea. Obstet Gynecol 1987; 69(1): 51-6.
6. Proctor ML, Smith CA, Farquhar CM, Stones RW: Transcutaneous electrical nerve stimulation and acupuncture for primary dysmenorrhoea. Cochrane Database Syst Rev 2002(1): CD002123.
7. Dieterle S, Ying G, Hatzmann W, Neuer A: Effect of acupuncture on the outcome of in vitro fertilization and intracytoplasmic sperm injection: a randomized, prospective, controlled clinical study. Fertil Steril 2006; 85(5): 1347-51.
8. Emmons S, Patton P: Acupuncture treatment for infertile women undergoing intracytoplasmic sperm injection. Medical Acupuncture: A Journal for Physicians by Physicians 2000; 12(2).
9. Johnson D: Acupuncture prior to and at embryo transfer in an assisted conception unit–a case series. Acupunct Med 2006; 24(1): 23-8.
10. Paulus WE, Zhang M, Strehler E, El-Danasouri I, Sterzik K: Influence of acupuncture on the pregnancy rate in patients who undergo assisted reproduction therapy. Fertil Steril 2002; 77(4): 721-4.
11. Westergaard LG, Mao Q, Krogslund M, Sandrini S, Lenz S, Grinsted J: Acupuncture on the day of embryo transfer significantly improves the reproductive outcome in infertile women: a prospective, randomized trial. Fertil Steril 2006; 85(5): 1341-6.
12. Smith C, Coyle M, Norman RJ: Influence of acupuncture stimulation on pregnancy rates for women undergoing embryo transfer. Fertil Steril 2006; 85(5): 1352-8.
13. Paulus WE, Zhang M, Strehler E, Seybold B, Sterzik K: Placebo-controlled trial of acupuncture effects in assisted repoduction therapy. Human Reprod 2003; 18(suppl 1): xviii18.
14. Cummings M: The terms ‘acupuncture’ and ‘placebo’ should be adequately defined in clinical trials. Complement Ther Med 2003; 11(2): 123; author reply 123-4.
15. Vickers AJ: Placebo controls in randomized trials of acupuncture. Eval Health Prof 2002; 25(4): 421-35.
16. Vincent C, Lewith G: Placebo controls for acupuncture studies. J R Soc Med 1995; 88(4): 199-202.
17. Lund I, Lundeberg T: Are minimal, superficial or sham acupuncture procedures acceptable as inert placebo controls? Acupunct Med 2006; 24(1): 13-5.
18. Anderson BJ, Rosenthal L: Acupuncture and IVF Controversies. Fertil Steril 2007; 87(4): 1000.
19. Anderson BJ, Haimovici F, Ginsburg ES, Schust DJ, Wayne PM: In vitro fertilization and acupuncture: clinical efficacy and mechanistic basis. Altern Ther Health Med 2007; 13(3): 38-48.
20. Suzuki H, Takahashi J, Kobayashi M, Ochi M: Nanchisei funinshou ni taisuru shinkyu chiryou no kentou 1 (Acupuncture treatment on intractable infertility – 1st report: Summary of 57 cases of insufficient endometrium lining treated with ART and acupuncture). Journal of the Japan Society of Acupuncture and Moxibustion 2002; 52(3): 309.
21. Takahashi J, Kobayashi M, Suzuki H, Ochi M: Nanchisei funinshou ni taisuru shinkyu chiryou no kentou – 2 (Acupuncture treatment on intractable infertility – 2nd report: Summary of 24 cases of idiopathic infertility treated with ART and acupuncture). Journal of the Japan Society of Acupuncture and Moxibustion 2002; 52(3): 310.
22. Nishijo K, Mori H, Tsukayama H, Yamashita H: Scientific Approach for Acupuncture. Journal of the Japan Society of Acupuncture and Moxibustion 1995; 45(3): 177-191.
23. Tanaka TH: The Possibilities for Optimizing Acupuncture Treatment Results through Synchronization with Somatic State: Examination of Autonomic Response to Superficial Needling During Exhalation. American Journal of Acupuncture 1996; 24(4): 233-239.
24. Bonica JJ: Applied Anatomy Relevant to Pain. In: Bonica JJ, ed. The Management of Pain, 2nd ed, vol Vol. 1. Pjiladelphia: Lea & Febiger, 1990; 133-158.
25. Uchida S, Hotta H, Kagitani F, Aikawa Y: Ovarian blood flow is reflexively regulated by mechanical afferent stimulation of a hindlimb in nonpregnant anesthetized rats. Auton Neurosci 2003; 106(2): 91-7.
26. Uchida S, Kagitani F, Hotta H, Hanada T, Aikawa Y: Cutaneous Mechanical Stimulation Regulates Ovarian Blood Flow via Activation of Spinal and Supraspinal Reflex Pathways in Anesthetized Rats. Jpn J Physiol 2005; 55(5): 265-77.
27. Hotta H, Uchida S, Shimura M, Suzuki H: Uterine contractility and blood flow are reflexively regulated by cutaneous afferent stimulation in anesthetized rats. J Auton Nerv Syst 1999; 75(1): 23-31.
28. Chang R, Chung PH, Rosenwaks Z: Role of acupuncture in the treatment of female infertility. Fertil Steril 2002; 78(6): 1149-53.
29. Schenker JG, Meirow D, Schenker E: Stress and human reproduction. Eur J Obstet Gynecol Reprod Biol 1992; 45(1): 1-8.
30. Lima AP, Moura MD, Rosa e Silva AA: Prolactin and cortisol levels in women with endometriosis. Braz J Med Biol Res 2006; 39(8): 1121-7.
31. Tanaka TH: The creation and efficacy of a HRV-Autonomic Trainer CD in assisting heart rate variability biofeedback training: preliminary report. Appl Psychophysiol Biofeedback 2003; 28(4): 326.
32. Lehrer P: Applied psychophysiology: beyond the boundaries of biofeedback (mending a wall, a brief history of our field, and applications to control of the muscles and cardiorespiratory systems). Appl Psychophysiol Biofeedback 2003; 28(4): 291-304.
33. Baker FC, Driver HS: Circadian rhythms, sleep, and the menstrual cycle. Sleep Med 2007; 8(6): 613-22.